1. Field of the Invention
The present invention relates generally to the field of food sweetener compositions, and relates specifically to the field of processes for manufacturing pectinic acid food sweetener compositions.
2. Description of Background Art
Aspartame is a non-nutritive sweetener that is 160 times sweeter than sucrose in aqueous systems. Because of its sweetness intensity, it is utilized in beverage systems at levels of between 5 mg percent and 200 mg percent by weight as a replacement for sucrose or other nutritive carbohydrates to produce a "low sugars" or "low-calorie" product. Almost three-fourths of all aspartame sales are made to the diet beverage industry.
The diet beverage industry, and more specifically the carbonated diet beverage industry, has preferentially utilized aspartame as the non-nutritive artificial sweetener. One drawback of aspartame is that many people detect a lingering aftertaste, frequently described as "metallic" or "bitter". Those people who detect an aftertaste with aspartame, and who currently do not consume the beverage because of the aftertaste, represent a substantial market. A low calorie product that does not possess the negative aftertastes perceived with aspartame potentially could gain a significant market share.
Chemical substances that diminish or eradicate the lingering aftertaste caused by aspartame, may be considered a food additive and therefore require FDA approval. Thus, compounds that already are considered GRAS (Generally Regarded As Safe) or are already approved by the FDA as a food additive, are preferable over those substances that must still go through the FDA review process.
Since the introduction of aspartame, many researchers have attempted to reduce the aftertaste using a variety of substances with limited success. One example is described in U.S. Pat. No. 4,690,827 to Kupper, et al. That patent discloses a process for increasing pulp volume (pulp composed of either homogenized fruit pulp, cellulose, or a cellulose/pectin material) in artificially sweetened beverages containing fruit juices. It was found that the increased pulp volume of reduced size apparently decreases the aftertaste of non-nutritional sweeteners, including aspartame, saccharine and cyclamate. The mechanism by which the aftertaste of these artificial sweeteners was diminished was not discussed other than the importance of increased pulp volume and decreased fruit pulp particle size. The increased pulp volume apparently had the same effect on all different types of artificial sweetener.
Plant cell wall material is a source of natural food ingredients used as thickeners and emulsifiers. Such plant cell wall material is composed of a broad group of polysaccharide compounds sometimes referred to as the hemicelluloses and gums. Hydrolysis of these polysaccharides yield mostly glucose, mannose, galactose, arabinose, or xylose. Glucuronic acid, mannuronic acid, guluronic, and galacturonic acid are also components of some hemicelluloses. Pectin and algin are examples of the latter group referred to as the polyuronide hemicelluloses. Polyuronides are also found in some gums. For example, gum karaya is slightly acidic and is believed to contain a polyuronic acid. Synthetic methods for the commercial preparation of polyuronic acids have been reported (U.S. Pat. No. 2,156,223, P. B. Myers) in the early part of this century, but are not currently commercially available.
In considering the gums and hemicelluloses which naturally contain polyuronic acids, the pectins and algin currently have the greatest commercial availability and importance. Alginic acid is isolated from several species of brown algae by alkaline extraction. It is composed of polymers of mannopyranosyluronic acid and L-guluronic acid units. Alginic acid, which is very slightly soluble in water, as well as the water soluble sodium, potassium, ammonium, calcium and magnesium salts of alginic acid (alginates), are commercial items of trade. Alginic acid holds GRAS status specifically for, and limited to, its use in soup and soup bases. The alginates also hold GRAS status and may be used at defined maximum use levels in a variety of food applications. Since algins are not commonly an endogenous part of foods and therefore are added specifically for the purpose of thickening, little work has been reported with regard to their thermal or enzymatic degradation or hydrolysis. However, it is generally known, that alginic acid is resistant to hydrolysis. Conversely, due to the existence of pectin in most fruits and vegetables, considerable work in the area of pectins has been reported.
Commercial pectin is a carbohydrate obtained by aqueous extraction of vegetables and fruits. The most common sources of pectin today are citrus fruit, apples, and sugar beet pulp. Pectin is considered to be a linear polysaccharide having a degree of polymerization (DP), which represents the number of building blocks or galacturonic acid units in a chain-like configuration, of from a few hundred to a thousand. This corresponds to average molecular weights from about 35,000 to about 150,000. The size of the polymer being a function of the source.
Food grade pectin is composed primarily of partially methoxylated polygalacturonic acid units and some neutral sugars such as arabinose, galactose, sorbose, and rhamnose. A recent article by J. Hwang, et al., (Food Hydrolloids, Vol. 7, no. 1, pages 39-53, 1993), describes the side-chains of pectins found in different sources of pectin. These side-chains include the pentosans rhamnogalacturonan and arabinan. These side-chains are found in abundance in n apple pectin. Pectin derived from sugar beets has also been found to have some acetyl groups associated with it. In general, depending upon the degree of esterification (DE), pectins normally are classified into low methoxyl and high methoxyl content. Pectin having a DE of less than 50% is considered to be low methoxyl pectin (LMP) and pectin containing greater than 50% methoxyl groups is considered to be high methoxyl pectin (HMP). Pectinic acids (PNA) are that group of pectins containing methoxyl groups in the theoretical range of DE5 to DE95. Commercial pectins which have not been subjected to de-esterification, are high methoxyl, having a DE typically between DE65 and DE75. Pectic acid (PA) is a polygalacturonic acid with no apparent esterification of the acid group and unlike the pectinic acids which are dispersible in water, are insoluble in aqueous solutions.
Pectin as an exogenous food ingredient product, has long been recognized and utilized exclusively for its bulking, gelling, emulsifying, and thickening properties. Its primary use has been in the glassed foods (jams/jellies), bakery products, pharmaceuticals, pet foods, confections, and beverages. On the other hand, endogenous pectin in the manufacture of some food products, because of its mucilaginous, colloidal, and thickening properties, is considered undesirable. Consequently, enzymatic and thermal means are employed to hydrolyze the pectin thereby reducing the viscosity and permitting un-obstructed filtration of the food material. Probably the largest use of enzymatic degradation of pectin is in the fruit juice industry where the mucilaginous property of undegraded pectin block or foul a filter. Fruit juice treated with a pectinase no longer possesses this mucilaginous or thickening characteristic thereby allowing the juice to be filtered by either ultrafiltration techniques or filtration using a filter aid such as diatomaceous earth.
In the past, different types of degradation of pectin have been studied in the literature. Physical methods include aging, heating, and freezing. Chemical based methods include enzymatic, oxidative, acid, and alkaline. At the present time, thermal and enzymatic degradation are of primary use and importance.
Thermal hydrolysis of pectin has been done primarily as an academic exercise to aid in the elucidation of the pectin structure and understanding viscosity changes. Studies were performed by Merrill and Weeks, J. Am. Chem. Soc., 67:224 (1945), by heating aqueous pectin solutions for a period of time up to 24 hours at a maximum temperature of 100.degree. C. Based on that study, they concluded that the decrease in viscosity of heated pectin solutions was due to the breaking of primary chemical valence bonds. Kertesz, The Pectic Substances, p. 146-151 (Interscience Publishers, Inc., New York, N.Y., 1951 ) later argued that heat does not hydrolyze the glycosidic bonds but rather disrupts an aggregate structure of the pectin.
Degradation in the presence of alkali were performed in an effort to understand the degradation reactions occurring in food products containing pectin. Keijbets, Carbohydrate Research, 33:359-362 (1974) summarized that the heating of plant tissues under alkaline conditions or at a pH greater than 4.0 will degrade the pectin molecules by beta-elimination. This work later was confirmed by Sajjaanantakul et al., J. of Food Science, Volume 54, No. 5, 1989, page 1272-1277.
Enzymatic hydrolysis of pectins has recently been used to economically reduce undesirable mucilaginous or thickening properties caused by the endogenous pectins. Pectinase as obtained commercially, is not pure and contains different types of polygalacturonase (PG), polygalacturonase lyase (PGL), and pectinmethylesterase (PE). The products of enzymatic pectin hydrolysis therefore are varied and include methanol as well as high levels of galacturonic acid and the methyl ester of galacturonic acid.
There remains a need for an improved sugar acid manufactured from pectin, and a process for manufacturing such a treated pectin.